A variety of mobile devices now exist which have the capability of determining their own location. Portable navigation devices (PNDs) that include GNSS (Global Navigation Satellite Systems) signal reception and processing functionality are well known and are widely employed as in-car or other vehicle navigation systems. Such devices include a GNSS antenna, such as a GPS antenna, by means of which satellite-broadcast signals, including location data, can be received and subsequently processed to determine a current location of the device. The device may also include electronic gyroscopes and accelerometers that produce signals that can be processed to determine the current angular and linear acceleration. The determined acceleration may then be used in conjunction with location information derived from the GPS signal to determine the velocity and relative displacement of the device and thus that of a vehicle in which it is mounted. Such sensors are most commonly provided in in-vehicle navigation systems, but may also be provided in the PND itself.
In recent years, GPS has also been used in systems to warn drivers of the incidence of speed traps, enforcement cameras and road hazards, such as school zones and locations in which there has been a relatively high frequency of accidents, known as “accident black spots”. In such systems, a device having a GPS antenna and access to a database containing the location of speed traps, accident black spots and other relevant items is typically provided in a vehicle. The device is configured to provide warnings to a driver when the vehicle, using the location information derived from the GPS signal, is in the vicinity of one of the locations stored in the database. One such system is described, for example, in WO 01/55744 A2.
Map data for electronic navigation devices, such as portable navigation devices as described above, comes from specialist map vendors. The data in these maps is specially designed to be used by route guidance algorithms, typically using location data from the GPS system. For example, navigable segments, such as roads, can be described as lines, i.e. vectors (e.g. start point, direction of road, with an entire road being made up of many hundreds of such segments, each uniquely defined by start point/end point direction parameters). A map is then a set of such vectors, data associated with each vector (speed limit; travel direction, etc.), and can further include points of interest (POIs), road names, other geographic features like park boundaries, river boundaries and the like, etc. All map features (e.g. vectors, POIs, etc.) are typically defined in a coordinate system that corresponds with or relates to the GPS coordinate system, enabling a device's position as determined through a GPS system to be located onto the relevant segment shown in a map for an optimal route to be planned to a destination.
Embodiments of the present invention aim to provide a method and apparatus for the improved notification of so-called accident black spots to a road user.